This invention relates to a tunnel kiln, more particularly to a construction of a tunnel kiln having a gate for kiln cars of which temperature is relatively low.
The term "gate" used herein means an inlet and/or an outlet for feeding a kiln car into or out of a tunnel kiln.
With hitherto used tunnel kilns to be used for example for firing molded ceramic green products, gates for kiln cars are positioned at relatively low temperatures (0.degree.-200.degree. C.). Therefore, in addition of usual kiln materials, gates of the kilns have been made of steel plate kiln materials of a unitary construction having a rectangular cross-section for example made to a carbon steel or a stainless steel.
In general, molded ceramic green products to be fired include molding aids added thereto, such as methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, starch paste and the like as binders and surface active agents, and waxes and the like as lubricants. These molding aids are decomposed at relatively low temperatures so that atmosphere gases in kilns usually include these molding aids as pyrolytically decomposed gases.
With the conventional kilns or kilns made of steel plate kiln materials, therefore, the pyrolytically decomposed gases in the atmosphere gases tend to attach to ceilings of the kilns so that the attached decomposed gases drop onto the ceramic products resulting in defective products. On the other hand, it is difficult to exhaust the pyrolytically decomposed distillate.